To answer this question, the user needs to understand the concept of software reliability.

Software reliability refers to the ability of a software system to perform its intended functions under stated conditions for a specified period of time.

Now, let's go through each option and explain why it is right or wrong:

A. Be easy to maintain: This option is not necessarily a requirement for software to be reliable. While maintainability is an important aspect of software development, it is not directly related to the system's reliability.

B. Be unlikely to cause a failure: This option is correct. Software should be designed and tested to minimize the likelihood of errors or failures. However, it is important to note that no software system can be completely immune to failure.

C. Never fail under any circumstances: This option is incorrect. It is impossible to create software that never fails under any circumstances. All software systems have limitations, and unexpected events can cause even the most reliable systems to fail.

D. Be written according to coding standards: This option is not directly related to software reliability. While coding standards can help improve the quality of software, they do not guarantee that the software will be reliable.

Therefore, the correct answer is:

The Answer is: B. Be unlikely to cause a failure.